CN106842034B

CN106842034B - Estimating battery capacity in an electric vehicle

Info

Publication number: CN106842034B
Application number: CN201610898977.9A
Authority: CN
Inventors: 王旭; 何川; 常晓光
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-10-14
Filing date: 2016-10-14
Publication date: 2020-10-27
Anticipated expiration: 2036-10-14
Also published as: DE102016119121A1; US10322634B2; CN106842034A; US20170106760A1

Abstract

The present disclosure relates to estimating battery capacity in an electric vehicle. Vehicles using electric power as power may use accurate measurements of battery power for a variety of purposes (e.g., battery characteristics, battery state of charge, remaining travel distance of the vehicle, etc.). Traction battery measurements should be taken when the battery is fully relaxed, i.e., when the battery is neither charging nor providing power, and after the battery chemistry has reached steady state for a period of time. The controller or method may determine whether the battery is slack and whether the battery is not slack, delaying the determination of whether to charge or discharge the traction battery to allow for accurate battery capacity. The controller may control the battery charger to ensure that the battery is fully relaxed before sensing the battery characteristics.

Description

Estimating battery capacity in an electric vehicle

Technical Field

The present disclosure relates generally to estimating battery capacity in an electric vehicle.

Background

Vehicles that use electric power as power rely on accurate measurements of battery capacity for a variety of purposes (e.g., battery characteristics, battery state of charge, remaining vehicle travel distance, etc.). Control strategies for charging and discharging traction batteries for Battery Electric Vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) continue to evolve to improve battery life and vehicle performance. The charge current and the discharge current applied to the battery cause a chemical reaction within the battery. Battery measurements taken before the battery chemistry has stabilized can lead to inaccurate determinations of various battery characteristics.

Disclosure of Invention

To improve the accuracy of the battery capacity estimation, the battery measurements may be taken when the battery is fully relaxed (i.e., when the battery chemistry reaches a steady state after the charging or discharging current is terminated). In one embodiment, the controller is configured to determine whether the battery is slack based on the stored battery profile and/or a battery slack timer. If the battery is not slack, charging the traction battery is delayed or power is withdrawn from the traction battery is delayed to improve battery measurement accuracy. The controller may control the battery charger to stop current flow to or from the battery to ensure that the battery is fully relaxed based on an expiration of an associated relaxation time prior to sensing the battery characteristic. The controller may be configured to immediately begin charging the traction battery if the traction battery is determined to be slack. The controller may be configured to store a battery profile for use in determining whether the traction battery is fully relaxed. The controller may be configured to: the charging is delayed for a period of time when the controller determines that the traction battery is not slack. When the battery capacity information is not available in a memory operatively connected to the controller, the controller may estimate the battery capacity after the elapse of the relaxation period.

In a representative embodiment, the controller uses the formula Ce ═ idt/(SOC)₁-SOC₂) Estimating a battery capacity, wherein SOC₁Is to know the state of charge, SOC, at the beginning₂Is to know the state of charge at the end. SOC₁And SOC₂At least a minimum relaxation time may be separated in time to ensure that the battery is in a relaxed state before the controller estimates the battery capacity. The controller may stop the estimation of the battery capacity when the battery temperature is below the battery temperature threshold.

According to the present invention, there is provided a vehicle including: a traction battery; a charger that charges the traction battery; a controller configured to: the method also includes controlling the charger to delay charging the traction battery during a battery relaxation time period that begins in response to battery current falling below a threshold, and measuring a first open circuit voltage of the traction battery after the delay and before charging of the traction battery to update a battery capacity value.

A method may be used to perform any of the above-described features of the controller. For example, a method may comprise: the traction battery is charged if it is determined that the battery is slack by expiration of the stored battery profile or associated slack time. If the battery is not relaxed, charging of the battery is delayed for a relaxation time period. The method may include setting a battery capacity based on a state of charge at a start of charging, a charging current, and a state of charge at an end of charging. If the traction battery is determined to be slack, charging may begin immediately. The method may include storing a battery profile having a minimum relaxation time as a function of battery temperature. When the battery capacity information is not available in the vehicle memory, the method may set the battery capacity after a period of time has elapsed.

In one example, the battery capacity setting includes using the formula Ce ═ idt/(SOC)₁-SOC₂) Wherein, SOC₁Is to know the state of charge, SOC, at the beginning₂Is to know the state of charge at the end. SOC₁And SOC₂At least a minimum relaxation time may be separated in time to ensure that the battery is in a relaxed state prior to setting the battery capacity. The method may include stopping the setting of the battery capacity when the battery temperature is below the battery temperature threshold.

According to the present disclosure, there is provided a method comprising: measuring, by the vehicle processor, a first traction battery open circuit voltage and a second traction battery open circuit voltage before charging the traction battery and after charging the traction battery, respectively, the first traction battery open circuit voltage and the second traction battery open circuit voltage being measured after expiration of the associated first battery relaxation time period and second battery relaxation time period; the battery capacity is set based on the accumulated battery charging current and first and second states of charge corresponding to the first and second open circuit voltages, respectively.

According to one embodiment of the present disclosure, the method further comprises charging the traction battery after expiration of the first battery relaxation time period.

According to an embodiment of the present disclosure, the method further comprises: the first and second battery relaxation time periods are retrieved by the vehicle processor from a memory associated with the vehicle processor, the first and second battery relaxation time periods being stored in the battery profile as a function of the battery temperature.

According to one embodiment of the disclosure, the step of setting the battery capacity occurs in response to the battery capacity information not being available in the vehicle memory.

According to one embodiment of the present disclosure, the step of setting the battery capacity: including according to Ce ═ idt/(SOC)₁-SOC₂) Setting the battery capacity, wherein SOC₁Is a first state of charge, SOC, associated with a first open circuit voltage₂Is a second state of charge associated with a second open circuit voltage.

According to one embodiment of the present disclosure, the first battery relaxation time period and the second battery relaxation time period are based on a lifespan of the traction battery.

According to the present disclosure, there is provided a vehicle including: a traction battery; a charger connected to the traction battery; a controller configured to: the battery capacity is updated based on a first SOC associated with a battery open-circuit voltage measured after a first battery relaxation time period before the battery is charged expires, a second SOC associated with a battery open-circuit voltage measured after a second battery relaxation time period after the battery is charged expires, and an accumulated battery charging current.

According to an embodiment of the disclosure, the controller is further configured to: delaying battery charging for a first battery relaxation time period after the battery current falls below the respective threshold.

According to one embodiment of the disclosure, the vehicle further includes a display screen in communication with the controller, the controller further configured to generate a message for display on the display screen in response to the delay.

According to one embodiment of the present disclosure, the controller is further configured to retrieve the first battery relaxation time period and the second battery relaxation time period from the memory based on the battery temperature.

According to one embodiment of the present disclosure, the first battery relaxation time period and the second battery relaxation time period are based on a battery lifespan.

Drawings

FIG. 1 is a schematic illustration of a vehicle at a charging station according to an exemplary embodiment;

FIG. 2 is a schematic illustration of a vehicle according to an exemplary embodiment;

FIG. 3 is a schematic diagram of a communication including a vehicle according to an exemplary embodiment;

FIG. 4 is a view of a vehicle interface according to an exemplary embodiment;

fig. 5 is a flowchart illustrating a method according to an example embodiment.

Detailed Description

As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely representative examples that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the claimed subject matter.

A vehicle (BEV) may be powered by a combination of battery power and a power source that includes battery power. For example, consider a Hybrid Electric Vehicle (HEV), in which the powertrain is powered by both the traction battery and the internal combustion engine. In these configurations, the traction battery is rechargeable and the vehicle charger provides power to restore the traction battery after discharge.

Referring to FIG. 1, a vehicle charging system, generally indicated by the numeral 110, is shown in accordance with one or more embodiments. Wired or inductive charging may be used to provide power from the vehicle charger 112 to the vehicle 100 to restore power to the traction batteries. In the representative embodiment shown, a charging station 116 is shown, the charging station 116 regulating the vehicle 100 to be charged by inductive charging. The vehicle 100 is parked at a charging station 116 that houses the vehicle charger 112. The vehicle charger 112 may be connected to receive household current such as is available in a typical home garage. Vehicle 100 may include a charging port 130, to which a charging cable from a charging station 131 may supply power to charge the traction battery.

The vehicle 100 includes a secondary coil housed in an inductive charging pad 118, the inductive charging pad 118 being disposed at the bottom of the vehicle 100. The secondary inductive charging pad 118 of the vehicle is electrically connected to the vehicle battery. The vehicle 100 also includes an AC-to-DC power converter to rectify and filter AC power received from the vehicle charger 112 to DC power to be received by the battery. The vehicle charger 112 is disposed in the floor under the vehicle 100 and includes a primary charging coil housed in a corresponding primary inductive charging pad 120. The primary inductive charging pad 120 is generally horizontal and located at a distance from the secondary inductive charging pad 118 of the vehicle. The primary inductive charging pad 120 may be adjustable in height to create a suitable gap to assist in charging of the vehicle 100. A current is supplied to the main coil, generating an electromagnetic field around the main inductive charge plate 120. When the vehicle's secondary inductive charging pad 118 is proximate to the powered-up primary inductive charging pad 120, the vehicle's secondary inductive charging pad 118 receives power by being in the generated electromagnetic field. A current is induced in the secondary winding and then transmitted to the vehicle battery. The gap between the plates allows for differences in vehicle alignment and also allows for adaptation to alternative authorized vehicles having different chassis heights.

In an alternative embodiment (not shown), the main inductive charging pad of the charging station is configured to be in a generally vertical position (e.g., on or near a vertical wall). The vehicle will have a corresponding secondary inductive charge plate on the front or rear vertical portion (e.g., as part of the front or rear bumper). When the vehicle enters the charging station and stops at the designated charging position, the main induction charging pad and the sub induction charging pad approach each other.

With continued reference to fig. 1, the vehicle 100 is provided with a controller 122. Although shown as a single controller, the vehicle controller 122 may include multiple controllers for controlling multiple vehicle systems. For example, the vehicle controller 122 may be a vehicle system controller/powertrain control module (VCS/PCM). In this regard, the vehicle charge control portion of the VCS/PCM may be software embedded in the VCS/PCM or may be a separate hardware device. The vehicle controller 122 generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM, and/or EEPROM), and software code to cooperate to perform a series of operations. The microprocessor in the vehicle controller 122 also includes a timer to track the elapsed time interval between the time reference and the selected event. The specified time interval is configured such that the processor provides a specific command signal and monitors the specified input at selectable time intervals. The vehicle controller is in electrical communication with a vehicle battery and receives a signal indicative of a battery charge level. The vehicle controller 22 also communicates with other controllers through a wired vehicle connection using a common bus protocol (e.g., CAN), and may also use wireless communication.

The vehicle charger 112 may be provided with a charger controller 124 having wireless communication capability. Similarly, the charger controller 124 has embedded software and is configured to regulate the flow of power provided by the vehicle charger 112. The software included in the charger controller 124 also includes a timer to track the time elapsed between specified events. In selected conditions, or upon receiving specified instructions, the charger controller 124 may enable, disable, or reduce the flow of power through the charger 112. The vehicle charger 112 is configured to receive a signal indicative of a charging instruction from the vehicle controller 122.

The vehicle controller 122 is configured to wirelessly communicate with the charger controller 124. Wireless communication may be accomplished via RFID, NFC, bluetooth, or other wireless methods. In at least one embodiment, wireless communication is used to complete the association procedure between the vehicle 100 and the vehicle charger 112 before starting the charging procedure. The association procedure may include the vehicle controller 122 sending a signal to the charger controller 124 indicating a request for authentication. The controller 122 then receives a response signal from the charger controller 124 and uses the response signal to determine whether the status of initial authentication granted to the vehicle charger 122 is agreed. Authentication may be affected by a number of specified factors, including manufacturer, power rating, security keys, and/or other authentication factors. Based on the appropriate response signals of the charger controller 124, the vehicle controller 122 determines a positive association between the vehicle 100 and the vehicle charger 112. Upon detecting an authenticated charger, the vehicle controller 122 provides an enable signal to the charger controller 124 to instruct the charging system to enable the charging process. The initial wireless request and subsequent authentication response constitute an association "handshake" between the two devices. The association also provides further secure communication and command signals between the vehicle 100 and the vehicle charger 112. If the vehicle controller 122 does not receive a positive authentication response, a command signal may be provided to prevent charging.

The vehicle controller 122 may also be configured to cause the generation of a plurality of warning signals. The vehicle 100 may be provided with a user display 126 inside the passenger compartment. User display 126 acts as a warning mechanism for the operator. The controller 122 may cause the generation of a plurality of different in-vehicle display messages. For example, a display alert may be generated to indicate that enhanced learning of battery capacity is being enabled. An enhanced learn warning may inform the operator that battery charging is to be delayed by the battery relaxation time. Other types of warnings (e.g., such as lights or illuminated graphical indicia) may be provided, for example, depending on the particular application and implementation.

As previously described, battery capacity may be used for various monitoring and control functions of the battery monitoring system. The battery capacity determines how much energy is stored in the battery and, therefore, the electric-only or EV-capable distance of travel of the electrified vehicle. Battery capacity may change as the battery ages, particularly when the battery is heavily used in PHEV/BEV applications. Accordingly, it would be desirable to provide a method or system that learns or adapts to battery capacity values over time. However, due to the related variations in battery chemistry, the time of measurement relative to the variations in battery charge/discharge current may affect the accuracy of the battery measurement used to determine battery capacity.

The battery capacity can be known or calculated according to the following equation:

wherein the SOC₁Is the initial state of charge (SOC) at which capacity learning begins (i.e., the SOC just prior to ampere-hour integration acquisition in the numerator), and SOC₂Is the final SOC (i.e., ampere just in the molecule) that completes the cell capacity learningIntegration of SOC after harvest during hours). The battery capacity learning using equation 1 may be applied while the vehicle is running (e.g., charge consumption mode in PHEV) and when the entry condition is satisfied or when the battery is charged from the grid. Representative entry conditions may include SOC₁And SOC₂The difference therebetween is more than 40%, and the driving time for which the change in SOC is more than 40% is not more than 1 hour, etc.

Open circuit voltage is an accurate indication of battery SOC of a lithium ion battery, often used as a vehicle traction battery. Therefore, SOC can be estimated from cell voltage₁And SOC₂. When the battery is fully relaxed for optimal accuracy, an open circuit voltage measurement should be taken. However, the operator usage patterns and associated battery control of the PHEV and BEV may not be conducive to measurements and capacity determinations based on a fully-relaxed traction battery. For example, an operator of the vehicle may drive the vehicle and arrive at the charging station 116. The vehicle 100 is aligned with a wireless charging system or immediately accesses a wired charging system 131. In another use case, the vehicle is charging and the operator starts driving the vehicle immediately after disconnecting from the charging system, e.g., driving off the wireless charger or unplugging the wired charging system 131 and driving the vehicle immediately. In these use cases, the chemistry of the traction battery may not have sufficient time to reach steady state (i.e., the battery does not fully relax), and the estimated capacity of the traction battery may be inaccurate if based on measurements taken before the battery fully relaxes.

Fig. 2 depicts an example of an electric vehicle (e.g., a plug-in hybrid electric vehicle). The plug-in hybrid electric vehicle 202 may include one or more electric motors 204 mechanically connected with a hybrid transmission 206. Furthermore, the hybrid transmission 206 is mechanically coupled to an engine 208 (e.g., an internal combustion engine). The hybrid transmission 206 may also be mechanically connected to a drive shaft 210, the drive shaft 210 being mechanically connected to wheels 212. The electric motor 204 may provide propulsion when the engine 208 is off, and the electric motor 204 may provide retarding capability when the engine 208 is on. The electric motor 204 may be configured as a generator and may provide fuel economy benefits by recovering energy that would normally be lost as heat in a friction braking system.

The traction battery 214 stores energy that may be used by the electric motor 204. The vehicle battery pack 214 typically provides a high voltage DC output. The traction battery 214 may include a battery pack having a plurality of battery cells. Traction batteries may be implemented by rechargeable batteries (e.g., lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium ion polymer batteries, and less common zinc-air batteries and molten salt batteries).

The battery 214 is electrically connected to the power electronics module 216. The power electronics module 216 is also electrically connected to the electric motor 204 and provides the ability to transfer energy bi-directionally between the battery 214 and the electric motor 204. For example, the battery 214 may provide a DC voltage, while the electric motor 204 may require a three-phase AC current to operate. The power electronics module 216 may convert the DC voltage to three-phase AC current required by the electric motor 204, for example, by using an inverter module. In the regeneration mode, the power electronics module 216 also converts the three-phase AC current from the electric motor 204 as a generator to the DC voltage required by the battery 214 using an inverter module or other circuitry. The methods described herein are equally applicable to electric only vehicles or any other device or vehicle that uses a battery pack.

During vehicle operation or when charging from a power source, the battery is in an active state where charging current flows into the battery or discharging current flows out of the battery, which causes a gradual change in the battery chemistry. Measurements of battery characteristics, such as open circuit voltage, are affected to varying degrees by these changes. The battery 214 transitions to a relaxed state in which the chemical composition has reached a steady state after a period of time in which no current is flowing into or out of the battery. As described above, the open circuit voltage measurement obtained after the battery chemistry reaches a steady state for the current condition and battery age (e.g., when the battery is fully relaxed) to determine the battery SOC is more accurate. The relaxation time required for the battery chemistry to reach steady state and for the battery to fully relax may vary based on, for example, the SOC, temperature, and battery chemistry of the battery. One or more battery profiles (profiles) may be stored in memory and used to determine an associated battery relaxation time or period in response to current battery and environmental conditions.

In addition to providing energy for propulsion, the battery 214 may provide energy for other vehicle electrical systems. Such a system may include a DC/DC converter module 218, the DC/DC converter module 218 converting the high voltage DC output of the battery pack 214 to a low voltage DC supply that is compatible with other vehicle loads. Other high voltage loads, such as a compressor and an electric heater, may be connected directly to the high voltage bus from the battery 214. In a vehicle, the low voltage system may be electrically connected to the 12V battery 220. An electric-only vehicle may have a similar structure, but without the engine 208. The power for the electrical accessories provided by the traction battery 214 places the battery 214 in an active state or an unrelaxed state.

The battery 214 may be recharged by an external power source 226. The external power source 226 may provide AC or DC power to the vehicle 202 through an electrical connection via the charging port 224. Charging port 224 may be any type of port configured to transmit power from external power source 226 to vehicle 202. The charging port 224 may be electrically connected to the power conversion module 222. The power conversion module 222 may condition power from an external power source 226 to provide a suitable voltage and current level to charge the battery 214. In some applications, the functionality of the power conversion module 222 may be present in the external power source 226. The vehicle engine, transmission, electric motor, battery, power conversion, and power electronics may be controlled by a power train control module (PCM) 228. As described above, current flows into the battery during charging, placing the battery 214 in an active state. The battery 214 transitions to a relaxed state after a period of time when no current flows to or from the battery 214. Battery capacity learning according to various embodiments of the present disclosure measures open circuit voltage when a battery relaxes to more accurately determine state of charge (SOC). The stored battery profile, which may include the battery SOC, temperature, and particular types of battery chemistries, may be used to determine an appropriate relaxation time corresponding to the current battery and/or ambient conditions.

In addition to showing a plug-in hybrid vehicle, FIG. 2 also represents a Battery Electric Vehicle (BEV) with the engine 208 removed. Similarly, fig. 2 may illustrate a conventional Hybrid Electric Vehicle (HEV) or a power split hybrid electric vehicle with

components

222, 224, and 226 removed. Fig. 2 also shows a high voltage system including an electric motor, a power electronics module 216, a DC/DC converter module 218, a power conversion module 222, and a battery 214. The high voltage system and the battery include a high voltage assembly including a bus bar, a high voltage connector, a high voltage line, and a current interrupt device. These high voltage components contribute to the resistance of the battery.

Fig. 3 shows a battery pack 214 configured by simply connecting N battery cell modules 302 in series. Battery cell module 302 may include a single battery cell or a plurality of battery cells electrically connected in parallel. However, a battery pack may consist of any number of individual cells and cell modules connected in series or parallel or some combination thereof. Each battery cell has an internal battery resistance. The system may have one or more controllers, such as a Battery Control Module (BCM)308 that monitors and controls the performance of the battery pack 214. The BCM 308 may monitor a plurality of battery pack level characteristics, such as battery pack current, battery pack voltage 310, and battery pack temperature 312, as measured by the current sensor 306. The current sensor 306 may be used to determine whether current is flowing to or from the battery, for example, to determine when the battery is in an active state. The active state may be determined when the current exceeds a corresponding non-zero threshold.

In addition to the level characteristics of the battery pack, the system may also monitor and control the level characteristics of the battery cells. For example, terminal voltage, current, and temperature of each battery cell or a representative subset of battery cells may be measured. The system may measure characteristics of one or more battery cell modules 302 using sensor modules 304. The characteristics may include cell voltage, temperature, age, number of charge/discharge cycles, and the like. In an example, the sensor module will measure the cell voltage. The cell voltage may be the voltage of a single battery or the voltage of a group of batteries electrically connected in parallel or series. The cell voltages may be based at least in part on connecting the cells to each other and toThe battery cells are connected to the electrical connections of other components. The battery 214 may utilize up to N_cThe individual sensor modules 304 measure a representative sample of the battery cells 302 or characteristics of all of the battery cells 302. Each sensor module 304 may transmit the measurements to BCM 308 for further processing and coordination. Sensor module 304 may transmit signals in analog or digital form to BCM 308. The battery 214 may also include a Battery Distribution Module (BDM)314, the Battery Distribution Module (BDM)314 controlling the flow of current into and out of the battery 214.

Fig. 4 shows a representative user interface 400 of the vehicle 100 for communicating the state of the vehicle to the operator, including SOC, state of charge, battery current, slack state of the battery, etc. According to embodiments of the present disclosure, the user interface 400 may also notify the operator to delay providing current to or from the battery to facilitate enhanced battery capacity determinations. User interface 400 may be presented by a vehicle control system in vehicle 100 via display 401 (e.g., a touch screen or LCD display). The user interface 400 may include a message prompt 402, the message prompt 402 informing the operator that an enhanced battery capacity determination is recommended. Depending on the particular application and implementation, the operator may be allowed to delay or cancel the determination via the user interface. In some embodiments, the message may be solely informative and not allow the vehicle operator to interrupt processing. As shown, a message prompt 402 is included in the user interface 400 as a message on top of other content of the user interface 400. It should be noted that in other examples, the message alert 402 may be provided in other forms (e.g., such as via a full-screen user interface, a light, or an illuminated graphic).

The user interface 400 may also include

controls

406, 408, and 410 configured to receive an indication from the user indicating whether the user agrees to allow vehicle time for battery relaxation to update the battery capacity. By way of example, the user interface 400 may include: a "yes" control 406 for receiving an indication from the user that the user agrees to a battery capacity update; a "no" control 408 for receiving an indication from the user that the user does not agree with the battery capacity update; and a "ask me later" control 410 for delaying the battery capacity update to a later date or time.

The user interface 400 may also be used to indicate to the user through the display 401 that a battery capacity update is suggested or has been successfully completed. The user interface 400 may indicate to the user that a battery capacity update is to be initiated at the next appropriate time period when the battery is in a relaxed state. The user interface 400 may also provide input controls to the user to cause modules in the vehicle to initiate battery capacity updates.

Fig. 5 illustrates operations of a system or method 500 for updating traction battery capacity of an electric vehicle or an electric assist vehicle. Battery capacity is a parameter used in traction battery monitoring systems. For example, battery capacity is used to generate an accurate estimate of state of charge (SOC), which may be provided as a percentage of battery capacity (e.g., based on voltage measurements). Battery capacity is also used in vehicles to determine how much energy is stored in the battery and thus the distance the vehicle can travel when powered by the battery alone. However, as described above, the battery capacity may change as the operating conditions and age change. Accordingly, methods and systems for learning capacity values over time may be used in electric vehicles. The battery capacity can be known by equation 1 presented above.

At 501, the vehicle determines that a battery capacity update is desired. The vehicle may be commanded from the external controller to initiate a battery capacity update by a corresponding message or flag stored in memory. In one example, the vehicle determines that the battery capacity of the vehicle should be updated. Various triggers may indicate to the vehicle that the battery capacity should be updated. In one embodiment, the BECM may determine that reported values of battery capacity, SOC, and/or open circuit voltage deviate from expected values based on an associated diagnostic routine. The vehicle may update the battery capacity based on the passage of the time period. The time period may vary depending on a variety of factors, such as battery age, number of charge/discharge cycles, and the like. In one example, the battery control module may maintain a timer to record how long has elapsed since the battery capacity was updated. At the beginning of battery life and at the end of life (where more variation is expected), the BECM may set shorter thresholds. For example, another trigger condition for battery capacity may be a reduction or loss of stored battery capacity (such as when the battery or control module is replaced).

For example, the current enhanced capacity learning may be performed when the vehicle is in a plug-in charging process or an inductive charging process (not charging from regenerative braking or from an internal combustion engine). If the vehicle is not in a plug-in charging process or an inductive charging process, method 500 may proceed to end 520. Otherwise, if a battery capacity update is desired (as indicated at 501) and the battery is ready to be charged from the plug-in or inductive charging system, an enhanced battery capacity update or learn routine is initiated (as indicated at 503). The battery capacity update may be initiated after an operator drives the vehicle and then stops the vehicle at a charging location near the inductive charging station or plugs a power plug into the vehicle.

At 505, the BECM or another vehicle controller determines if the battery is fully relaxed. As described above, battery relaxation is related to the battery chemistry approaching a steady state or equilibrium state after the battery current drops to zero or near zero (such as in the milliamp range), for example. The relaxation time may depend on a number of factors, such as the battery current before relaxation (higher current may require longer relaxation time), battery temperature, cell voltage, battery age, number of charge and/or discharge cycles, and the like. In one example, the cell voltage relaxes to a value within 90% of its final stable value within 5 seconds. The battery may be determined to be fully relaxed based on empirical data and corresponding thresholds, such as 90% or 95% of the final value. For example, empirical data and corresponding thresholds may be captured in a battery profile or look-up table stored in memory and accessible through one or more battery parameters, vehicle parameters, or environmental parameters (such as battery temperature and final battery current) to determine the relevant battery relaxation time. For example, different thresholds may be used to determine the degree of battery relaxation (such as 80% of the final voltage value corresponding to partial relaxation and 95% of the final voltage value corresponding to full relaxation). A battery is considered to be fully relaxed if the elapsed time since the battery current was zero or below a minimum threshold exceeds a minimum battery relaxation time (e.g., a few minutes, or up to a few tens of minutes).

As described above, the open circuit voltage measurement may be used to derive an SOC parameter, which in turn may be used to determine battery capacity according to equation 1. SOC₁And SOC₂May be estimated from the cell open circuit voltage, which is measured or otherwise determined after the battery is determined to be fully relaxed 505. In one embodiment, the BECM or another controller determines that the battery is fully relaxed based on expiration of a relaxation time triggered in response to the battery current falling below a corresponding threshold. The slack time may be determined from a stored battery profile or look-up table that may be accessed by the battery, vehicle and/or ambient operating parameters (e.g., such as battery current, battery temperature, ambient temperature, cell voltage, etc.).

If the battery relaxation time period specified by the battery profile and the current operating conditions has not expired such that the battery is not fully relaxed (as determined at 505), the vehicle may notify the operator via a communication means (e.g., display 400) that the charging or other operation of the vehicle is to be delayed to facilitate enhanced battery capacity calculations. In various embodiments, the operator may ignore the update or confirm the battery capacity update. Embodiments may also include notification messages that do not allow the operator to suspend or delay updates through a display or other user interface. In one embodiment, the message to the operator is "enhanced capacity learning to run. Charging will start after XX seconds. ". Similar reporting messages may be provided. For example, the display 400 may indicate "battery diagnostics are being performed and will be completed soon". The message will communicate to the operator that a delay in the availability or charging of the battery operated accessory will occur.

The battery current for charging or discharging may be delayed for a battery relaxation period (as represented at 509) to allow the battery chemistry to stabilize and perform enhanced battery capacity determinations. Battery charging (including trickle charging) is delayed for a battery relaxation time period and processing returns to step 505 to determine if the battery relaxation time has expired to indicate if the battery is fully relaxed. The plurality of programmable charging features may allow battery relaxation to be accomplished without notifying an operator. For example, battery charging may be configured to occur during the night to take advantage of the preferential electricity rates. In this case, the enhanced battery capacity determination may be started at a predetermined time before the scheduled battery charging is started or at a predetermined time after the scheduled battery charging is completed.

When the battery is fully relaxed (as indicated at 505), enhanced battery capacity learning may begin. The battery open circuit voltage may be determined (as indicated at 511) to provide the SOC based on a predetermined relationship stored in memory₁The exact value of (c). The battery control module will then close the charging contacts and begin charging the battery (as indicated at 513) and calculate the current integral as expressed in the numerator of equation 1. To minimize the error in the current integral ^ idt, the maximum available charging power that the charger can provide is used, since the shorter the charging time, the smaller the cumulative current integral error. The charging energy flows into the battery until the battery reaches a battery charging voltage threshold, and the charging process stops. The battery charge voltage threshold varies for different battery types and may be stored in memory associated with one or more vehicle processors.

After the battery is charged, the battery control module reads the previously stored SOC from the associated non-volatile memory₁And ^ idt. The open circuit voltage is again measured (as indicated at 515) and the SOC is obtained from a stored open circuit voltage to SOC relationship or look-up table based on the open circuit voltage measurement₂The value of (c). With these parameters, the battery capacity may then be calculated, for example, at 517 using equation 1. Thereafter, the process ends at 520.

There are many cases where the battery may not be plug-in charged or the charging process is terminated before the battery capacity determination is completed. In this case, the battery capacity learning is automatically terminated. If battery capacity learning is terminated, the battery control module will reset the process and will later be satisfied based on the entry conditions described aboveAttempts to update the battery capacity. In another example, if the SOC is based on the open circuit voltage after the battery is fully charged₂Less than the predefined value, the battery control module may reject the battery capacity update. Similarly, if the SOC is based on the open circuit voltage before the battery is charged₁If greater than the predefined value, the battery control module may reject the battery capacity update. Since battery capacity may be a function of temperature, the process may terminate, for example, if the battery temperature is below a temperature threshold.

While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the claimed subject matter. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Furthermore, features of various implementing embodiments may be combined to form further embodiments within the scope of the claims, which are not explicitly shown or described.

Claims

1. A vehicle, comprising:

a traction battery;

a charger for charging the traction battery;

a controller configured to: controlling the charger to delay charging the traction battery for a battery relaxation time period after a current of the traction battery falls below a threshold value, and measuring a first open circuit voltage of the traction battery after the battery relaxation time period and before resuming charging of the traction battery to update a battery capacity value based on the first open circuit voltage,

wherein the controller is further configured to: retrieving a stored value for the battery relaxation time period based on a temperature of the traction battery, a time of existence of the traction battery, and a state of charge of the traction battery.

2. The vehicle of claim 1, wherein the controller is configured to: retrieving the stored battery profile to determine the battery relaxation time period.

3. The vehicle of claim 1, wherein the controller is configured to: a second open circuit voltage is measured after traction battery charging has been completed, and a battery capacity value is updated based on the first and second open circuit voltage measurement values.

4. The vehicle of claim 1, wherein the controller is configured to: updating a battery capacity value based on a first battery state of charge associated with the first open circuit voltage.

5. The vehicle of claim 1, wherein the controller updates the battery capacity value in response to previously stored battery capacity information being unavailable.

6. The vehicle of claim 1, wherein the controller is configured to: using the formula Ce ═ idt/(SOC)₁-SOC₂) Updating battery capacity, wherein SOC₁Is the initial state of charge, SOC, at the beginning of capacity learning₂Is the final state of charge at the end of capacity learning.

7. The vehicle of claim 6, wherein the controller measures a second open circuit voltage after a second battery relaxation time period that begins in response to completion of charging of the traction battery and determines the SOC based on the second open circuit voltage₂。

8. The vehicle of claim 1, wherein the controller stops the updating of the battery capacity value in response to a battery temperature being below a battery temperature threshold.